The aims of this study were, firstly, to identify different groups of teacher-child dyads on the basis of the longitudinal associations between teachers’ individual support in reading and children’s reading skills, and, secondly, to examine whether the groups thus identified differ with respect to various teacher- and child-related factors. A total of 372 teacher-child dyads were examined. The reading skills of 6- to 7-year-old Finnish-speaking children were measured at the beginning and end of Grade 1. The amount of teachers’ support in reading for a particular child was gathered from teachers by questionnaires. Regression Mixture Modeling identified three latent groups of teacher-child dyads: Among 38% of the dyads, teachers’ increased support in reading for a particular child positively predicted the development of the child’s reading skills; among 13% of the dyads, teachers’ support in reading had no association with the child’s reading skills; and among the remaining 49% of the dyads, children acquired reading skills slowly irrespective of teachers’ efforts to support their learning. Teachers’ individual support in reading was positively related to the reading skills for children who were initially interested in reading, and who showed low levels of externalizing problem behavior. Moreover, teachers experienced less negative affect and reported less teaching-related stress when supporting children whose reading skills were developing faster in respect to reading instruction (vs. when working with children whose acquisition of reading skills developed more slowly).