
444 S.E.2d 643 (1994)
115 N.C. App. 249
STATE of North Carolina
v.
Jerry Wayne ROBERTSON.
No. 9318SC743.
Court of Appeals of North Carolina.
June 21, 1994.
*646 Atty. Gen. Michael F. Easley by Sp. Deputy Atty. Gen. George W. Boylan, Raleigh, for State.
Neill A. Jennings, Jr., Greensboro, for defendant-appellant.
EAGLES, Judge.
Defendant brings forward several assignments of error. After carefully reviewing the record and briefs, we conclude that the trial court committed no error.

I.
Defendant first contends that the trial court erred in allowing the victim to testify that defendant threatened her by saying, "[I]f [she] told anybody what he [defendant] was going to do, he was going to hurt [her] like he hurt Koda." The trial court allowed this testimony despite its previous ruling allowing defendant's motion in limine to prohibit reference to defendant's prior arrest, indictment, trial and acquittal of the murder of Koda Smith.
At the time of the events alleged here, defendant was under indictment and on pre-trial release for the murder of Aileen Koda Smith. Defendant was subsequently acquitted of that charge. Prior to trial here, defendant filed a motion in limine to exclude any reference to Koda Smith or her death or defendant's arrest, indictment and trial for her murder. The trial court granted defendant's motion to prohibit mention of defendant's arrest, indictment and trial for the alleged murder of Koda Smith, but denied defendant's motion to prohibit reference to the name Koda Smith. The victim testified at trial that defendant threatened her by saying, "[I]f [she] told anybody what he [defendant] was going to do, he was going to hurt [her] like he hurt Koda." Defendant contends that the trial court should have excluded the reference to "Koda" in the victim's testimony under Rule 403 of the North Carolina Rules of Evidence. We disagree.
Rule 403 provides:
Rule 403. Exclusion of relevant evidence on grounds of prejudice, confusion, or waste of time.
Although relevant, evidence may be excluded if its probative value is substantially outweighed by the danger of unfair prejudice, confusion of the issues, or misleading the jury, or by considerations of undue delay, waste of time, or needless presentation of cumulative evidence.
Whether evidence should be excluded under Rule 403 is ordinarily a decision within the trial court's discretion. State v. Meekins, 326 N.C. 689, 700, 392 S.E.2d 346, 352 (1990). Defendant relies on State v. Scott, 331 N.C. 39, 413 S.E.2d 787 (1992), in which the Supreme Court held that:
[E]vidence that defendant committed a prior alleged offense for which he has been tried and acquitted may not be admitted in *647 a subsequent trial for a different offense when its probative value depends, as it did here, upon the proposition that defendant in fact committed the prior crime. To admit such evidence violates, as a matter of law, Evidence Rule 403.
Id. at 42, 413 S.E.2d at 788. We find Scott distinguishable.
In Scott, supra, the defendant was indicted on charges of second degree kidnapping, crime against nature, and three counts of second degree rape. The State's evidence at trial tended to show that defendant approached the victim at a convenience store and asked her for a ride home. The victim was already acquainted with the defendant and agreed to take him home. When they left the parking lot, the defendant threatened the victim with a knife and raped her.
At issue in Scott was the testimony of Wanda Freeman, a past acquaintance of defendant, who testified that defendant had raped her two years earlier under similar circumstances. Defendant objected on the grounds that he had been tried and acquitted of Freeman's rape by a jury. In holding that Freeman's testimony violated Rule 403 as a matter of law, the Supreme Court stated:
When the probative value of evidence of this other conduct depends upon the proposition that defendant committed the prior crime, his earlier acquittal of that crime so erodes the probative value of the evidence that its potential for prejudice, which is great, must perforce outweigh its probative value under Rule 403.
Scott, 331 N.C. at 44, 413 S.E.2d at 790. The Scott court concluded that the probative value of Freeman's testimony depended upon the proposition that defendant had actually raped Freeman two years earlier. Defendant's acquittal of Freeman's rape so eroded its probative value that it was "substantially outweighed by the danger of unfair prejudice" as a matter of law.
Here, the probative value of defendant's statement does not depend on the proposition that defendant in fact hurt Koda. The victim testified that she did not scream or make any loud noises because defendant had threatened to hurt her. The probative value of defendant's statement was to show that the victim was scared of defendant as well as why she did not scream or make any noise. Accordingly, we conclude that Scott does not control here.
The State contends that defendant's statement is admissible under State v. Agee, 326 N.C. 542, 391 S.E.2d 171 (1990), as part of the "chain of circumstances" establishing the context of the crime charged. We agree. "[A]dmission of evidence of a criminal defendant's prior bad acts, received to establish the circumstances of the crime on trial by describing its immediate context,.... is admissible if it `forms part of the history of the event or serves to enhance the natural development of the facts.'" Id. at 547, 391 S.E.2d at 174 (citations omitted). In Agee, defendant was on trial for felonious possession of LSD. The arresting officer testified that he stopped defendant's vehicle for weaving on the road. When the officer approached the car, defendant made a threatening remark. The officer called for backup and when backup arrived, the officer searched defendant's person for weapons. During the search, the officer found a bag of marijuana in defendant's pocket. After finding the marijuana, the officer searched the vehicle and found the LSD. Defendant objected to the officer's testimony about finding the marijuana in defendant's pocket because defendant had previously been acquitted of possessing that marijuana in another trial. In holding that the officer's testimony was admissible, the Supreme Court stated:
Evidence, not part of the crime charged but pertaining to the chain of events explaining the context, motive and set-up of the crime, is properly admitted if linked in time and circumstances with the charged crime, or [if it] forms an integral and natural part of an account of the crime, or is necessary to complete the story of the crime for the jury.
Agee, 326 N.C. 542, 548, 391 S.E.2d 171, 174 (1990) (quoting United States v. Williford, 764 F.2d 1493, 1499 (11th Cir.1985)).
Here, the victim testified to defendant's statement during her account of the crime. In describing how she was sexually assaulted, the victim testified that defendant put his *648 hand over her mouth and told her that "[I]f [she] told anybody what he [defendant] was going to do, he was going to hurt [her] like he hurt Koda." We conclude that defendant's statement here formed an "integral and natural part" of the victim's account of the crime and was "necessary to complete the story of the crime for the jury." Cf. Agee, supra. Accordingly, the trial court did not err in allowing defendant's statement.

II.
Defendant next contends that the trial court erred in allowing the State's medical expert, Dr. Martha K. Sharpless, to testify to statements the victim made to her about the incident during a physical examination of the victim. Defendant contends that Dr. Sharpless' testimony was inadmissible hearsay because the victim's statements to Dr. Sharpless were not made for the purposes of medical diagnosis or treatment as required by G.S. 8C-1, Rule 803(4).
We need not address whether the victim's statements to Dr. Sharpless fall within the "Statements for Purposes of Medical Diagnosis" exception to the hearsay rule because the trial court admitted Dr. Sharpless' testimony only for the limited purpose of corroborating the in-court testimony of the victim. "Evidence which is inadmissible for substantive or illustrative purposes may nevertheless be admitted as corroborative evidence in appropriate cases when it tends to enhance the credibility of a witness." State v. Burns, 307 N.C. 224, 229, 297 S.E.2d 384, 387 (1982). Dr. Sharpless' testimony essentially corroborated the earlier testimony of the victim, including the defendant's threat to the victim. We also note that defendant objected "except for purposes of corroboration." The trial court then properly instructed the jury that Dr. Sharpless' testimony was only to be received "for the limited and narrow purpose of corroborating the in-court testimony" of the victim. Accordingly, this assignment of error is overruled.

III.
Defendant next contends that the trial court erred in permitting the State to impeach defendant by asking defendant whether he had a midnight curfew. The following exchange took place between the assistant district attorney and defendant during defendant's cross examination:
Q. At some point Chris [Creed] and Danielle [Johnson] left; is that right?
A. Yes, sir. I don't know where they were going.
Q. What time was it by then?
A. I couldn't tell you what time it was. They was getting ready to go somewhere and Chris just said stay here and talk to Donna till we get back.
Q. It was after midnight by then, wasn't it?
A. I don't know what time it was. I'm not sure.
Q. Could it have been after midnight?
MR. JENNINGS: Object. Asked and answered, Your Honor.
THE COURT: Overruled.
A. It might have been. It might not have been. I do not know.
Q. You weren't concerned at all about what time it was?
A. No, sir. I don't see what reason there was to be.
Q. Well, didn't you have a midnight curfew?
A. Huh?
MR. JENNINGS: Object.
Q. Didn't you have a midnight curfew?
THE COURT: Overruled.
A. Not that I remember. I don't remember having no midnight curfew.
At the time of the incident, defendant was subject to a midnight curfew as a condition of his pre-trial release. Since defendant testified that he did not remember having a midnight curfew, the State threatened, out of the presence of the jury, to impeach defendant with his pre-trial release papers which indicated that defendant was under a "12:00 midnight curfew Friday and Saturday." The trial court conducted a voir dire out of the presence of the jury and allowed the State to show defendant the pre-trial release papers and refresh defendant's memory that he was indeed under a midnight curfew at the time *649 of the incident. Defendant contends this constituted improper impeachment under Rule 608(b) of the North Carolina Rules of Evidence. We disagree.
Rule 608(b) provides:
(b) Specific instances of conduct.Specific instances of the conduct of a witness, for the purpose of attacking or supporting his credibility, other than conviction of crime as provided in Rule 609, may not be proved by extrinsic evidence.
Here, extrinsic evidence was not used to impeach defendant before the jury. Defendant was shown his pre-trial release papers outside of the presence of the jury. Defendant's cross examination in the presence of the jury resumed as follows:
Q. (By Mr. Neumann) [Defendant], I'll ask you again if you've had some time to reflect on it whether you were under a midnight curfew on this particular night?
A. Yes, sir. My memory is refreshed.
Q. I believe you earlier said you weren't concerned with what time it was?
A. No, sir. I had no business
MR. JENNINGS: Object.
A. no reason to.
THE COURT: Overruled.
Q. So, you didn't care if you missed your midnight curfew or not, did you?
A. I didn't remember having one.
Q. You remember now, don't you?
A. Yes, sir.
No extrinsic evidence of defendant's pre-trial release was admitted before the jury. Accordingly, we conclude that defendant was not improperly impeached under Rule 608(b). Defendant also contends that the question "Didn't you have a midnight curfew," violated the court's ruling on defendant's motion in limine to exclude references to defendant's prior arrest, indictment, trial and acquittal of the murder of Koda Smith. However, since there is no indication that the jury was aware of defendant's prior arrest, we conclude that the jury could not have reasonably inferred that defendant, at age 17, was under anything other than a traditional parental curfew during the night in question.

IV.
Defendant next contends that the trial court erred in excluding the testimony of defendant's expert psychologist, Dr. John F. Warren, on the suggestibility of child witnesses. We disagree.
Dr. Warren was certified by the trial court as an expert in clinical psychology and human behavior. Defendant offered Dr. Warren's testimony on the phenomenon of suggestibility. On voir dire, Dr. Warren testified that suggestibility is the "altering or the creation of memories through questions, gestures, other stimuli that happen around the person who is doing the remembering." Dr. Warren would have also testified that suggestibility is significant in young children or intellectually impaired persons. Defendant offered Dr. Warren's testimony to show that the victim's memory may have been created or altered through suggestion.
Under Rule 702 of the North Carolina Rules of Evidence, expert testimony is admissible if it will appreciably help the jury. State v. Knox, 78 N.C.App. 493, 495, 337 S.E.2d 154, 156 (1985). In applying this test, the trial court must balance the probative value of the testimony against its potential for prejudice, confusion, or delay. Id.; G.S. 8C-1, Rule 403. The trial court has wide discretion in determining whether expert testimony is admissible. Knox, 78 N.C.App. at 495, 337 S.E.2d at 156.
Here, Dr. Warren testified that he did not ever examine or evaluate the victim or anyone else connected with this case. On these facts, the trial court could properly conclude that the probative value of Dr. Warren's testimony was outweighed by its potential to prejudice or confuse the jury. Similarly, we are not persuaded that Dr. Warren's testimony would have "appreciably aided" the jury since he had never examined or evaluated the victim. Accordingly, we conclude that the trial court did not abuse its discretion in excluding Dr. Warren's testimony.

V.
Defendant's next three contentions concern the sentencing phase of the trial. Defendant first contends that the trial court *650 erred in failing to find defendant's immaturity as a mitigating factor. G.S. 15A-1340.4(a)(2)e allows a defendant's immaturity to be considered as a mitigating factor if the defendant's immaturity "at the time of commission of the offense significantly reduced his culpability for the offense." At the time of the offense, defendant was seventeen years old and a high school drop out. In refusing to find defendant's immaturity as a mitigating factor, the trial court stated, "This is a man that just went out and got married and took on the responsibilities for a wife and two children.... That doesn't smack of immaturity." Defendant contends that the trial court erred in evaluating defendant's immaturity at the time of trial instead of at the time of the commission of the offense. We disagree.
A trial court has wide discretion in determining the existence of mitigating factors because it "observes the demeanor of the witness and hears the testimony." State v. Heatwole, 333 N.C. 156, 163, 423 S.E.2d 735, 739 (1992). Immaturity as a statutory mitigating factor requires two inquiries: One as to immaturity and one as to the effect of that immaturity upon culpability. State v. Moore, 317 N.C. 275, 280, 345 S.E.2d 217, 221 (1986). Age alone is insufficient to support this factor. Id. The fact that defendant is seventeen years old, without more, does not classify defendant as immature under the statute. Id. As to the second inquiry, defendant presented no evidence on the effect of his immaturity upon his culpability for the offense. It is within the trial court's discretion to assess whether a defendant's immaturity significantly reduced his culpability for the offense. Id. at 281, 345 S.E.2d at 221. Accordingly, we conclude that the trial court did not abuse its discretion in failing to find defendant's immaturity as a mitigating factor.
Second, defendant contends the trial court erred in finding as an aggravating factor that defendant committed the offenses while on pre-trial release for a felony charge. G.S. 15A-1340.4(a)(1)k. Defendant contends that since he has been acquitted of the prior charge, the fact that he was on pre-trial release during the commission of these offenses cannot be used to aggravate his sentence. Based on State v. Webb, 309 N.C. 549, 308 S.E.2d 252 (1983), we disagree.
The rationale underlying G.S. 15A-1340.4(a)(1)k is that, "[o]ne demonstrates disdain for the law by committing an offense while on release pending trial of an earlier charge." Webb, 309 N.C. at 559, 308 S.E.2d at 258.
Whether or not one [on pre-trial release] is in fact guilty, it is to be expected that he would, while the question of his guilt is pending, be particularly cautious to avoid commission of another criminal offense. If he is not and is convicted of another offense, his status as a pretrial releasee in a pending case is a legitimate circumstance to be considered in imposing sentence.
Id. The fact that defendant was subsequently acquitted of the prior charge does not undermine the rationale for finding as an aggravating factor that defendant committed this offense while on pre-trial release. Accordingly, the trial court did not abuse its discretion in this regard.
Finally, defendant contends that the trial court erred in imposing a sentence greater than the presumptive term. Defendant contends that the trial court erred in finding that the one aggravating factor of committing the offenses while on pre-trial release outweighed the one mitigating factor that defendant had no prior record of convictions. Defendant's contention is without merit. The task of weighing aggravating and mitigating factors is discretionary and is not simply a matter of mathematics. State v. Melton, 307 N.C. 370, 380, 298 S.E.2d 673, 680 (1983). The trial court may properly emphasize one factor over another in weighing these factors. Id. We conclude that the trial court did not abuse its discretion in sentencing defendant.

VI.
For the reasons stated, we conclude that defendant received a fair trial free from prejudicial error.
No error.
MARTIN and McCRODDEN, JJ., concur.
