This article describes a study on mutuality in mother-child interaction during reading and playing sessions. Within mother-child interaction, mutuality is seen as important in language acquisition. The study was executed within a group of Netherlands Antillean mother-child dyads who participated in an intervention programme. Mutuality was operationalised as balance in conversation, joint involvement, affection, and more practical elements such as asking questions. Twelve participants were observed at least once. In five cases, repeated measures were also collected. Group data revealed that only few differences exist between the outcomes of the reading and playing sessions. The differences that were found, concerning balance and affection, were favourable to the play situations. However, large inter- and intra-individual differences were found in all observed measures of mutuality, which suggests the importance of idiographic research methods. The practical implication is that researchers and interventionists should be sensitive to individual differences and be careful with applying group data to individuals.