Objective: To develop and validate a form for Documentation of Occupational Therapy Session during Intervention (D.O.T.S.I) based on the OTPF. This form may fill the need for more consistent and detailed documentation of the intervention process. Method: Fifty five pediatric OT's documented 2-3 treatment sessions. A total of 120 treatment sessions were recorded. Construct validity was assessed through known-groups differences, once based on age groups and once based on context groups. Results: Significant inter-rater reliability in most sub-categories was found with a good Cronbach alpha coefficient. Construct validity was established by significant differences between the two settings (educational and clinic) and the two age groups. Conclusion: The D.O.T.S.I. form as a reliable and valid measure enables to simply document intervention in a unified and professional method. The documentation method of the D.O.T.S.I. stimulates clinical reasoning by allowing the therapist to reflect on the process of intervention and plan future progress. (Contains 1 figure and 4 tables.)