This review examines which types of instruction in writing-to-learn lead to effects on insight and topic knowledge in different disciplines, in grades 5-12 and in higher education. Forty-three empirical studies have been selected to answer this question. Four types of instruction are distinguished. Three of them are based on hypotheses proposed by Klein (1999) about the cognitive processes involved in writing-to-learn: Forward Search, Genre Writing and Backward Search. The fourth type, Planning Only, arises from the literature reviewed. Results of the studies show that about two thirds of the (quasi) experimental studies lead to positive effects on insight and topic knowledge for the four types of instruction. However, given the small number of experimental studies conducted, no firm conclusions can be drawn for three types of instruction. For the remaining type of instruction, Genre Writing, a larger number of studies provide positive evidence. Suggestions for future research are discussed.