The psychological-pedagogical problem of computer usage as a means for diagnostics of child's intellectual development is discussed. The characteristics of exercising analysis by 12- 13 years old schoolchildren were studied and psychological requirements to the methods of this action study formulated. The usage of a computer in such a diagnostics is substantiated. The effectiveness of computer usage in diagnostics of comprehension is due to the possibility of exteriorization of analysis (planning and reflection as well). The process can be fixed to enable the participants to realize it.