Students involved in holistic technological practice need to develop an understanding of technological practice outside the classroom and to participate in tasks set as close as practicable to actual technological practice. This paper investigates the context of assessment and its relationship to achievement and the importance of teacher knowledge to student technological practice. I argue that "out of context" assessment tasks do not give an accurate indication of achievement levels of the children assessed. Introduced is the Model of Student Technological Practice, which identifies four constraints that influence student technological practice. A significant factor is teacher knowledge, as it impacts greatly on the quality of feedback given to students by their teachers. Timely teacher intervention and formative assessment feedback will alter student technological practice and should improve the students' likelihood of developing successful outcomes.