In the process of school self-evaluation (SSE), teachers are often asked to provide information on the school's functioning by completing questionnaires. However, respondents can leave one item or a series of items unanswered, after which they continue completing the questionnaire. This phenomenon of item nonresponse is not necessarily problematic if it occurs randomly. This study examines to what extent item nonresponse depends on respondents' motivation to fill in the SSE questionnaire, their tendency towards socially desirable responses, the evaluation perspective on the SSE, the item design, and the construct that the item aims to shed light on. This study reports on an experimental study with 376 respondents who completed a questionnaire in an authentic SSE setting. Cross-classified multilevel modelling identified that respondents' autonomous motivation predicts item nonresponse. Also, the evaluation perspective on SSE, item design, and the construct the item tends to capture all affect the probability of item nonresponse.