Stupid spirometer question

If a spirometer is properly working (sincroniced or whatever its called/spelled), is it possible for it to wrongly record a too high number based on a child's improper technique? I can see a low number being wrong or not an accurate assessment because the technique is wrong, but is it possible for a high number (that isn't repeatedable, because of youth and inability to consistently do a good technique), to be wrong or inaccurate based on technique? Or can you assume if there are 6 blows and one is high and the others all low, the high is the "correct" one and the lows are based on inconsistent/inaccurate technique? Thanks!!
Source: Cystic Fibrosis Adults Forum - Category: Respiratory Medicine Authors: Tags: Adults Source Type: forums