A previous study suggested that children use their own informal problem solving methods; based on counting procedures or mental calculation. Children’s counting skills and aspects of memory in relation to their ability to complete addition and subtraction problems were examined across a wide age range. The results showed that subjects with good mathematical ability had well developed schema about number and applied this in abstract processing of information when solving problems. Subjects with poor mathematical ability had little understanding of number, only procedural knowledge and used concrete counting procedures in problem solving to find an answer. Children’s information processing skills are discussed in terms of memory, schema theory and the role of self concept in controlling mental processes. A remedial teaching programme based on developing abstract information processing skills was trialled over a six week period with some success. The need for implementation of research findings into classroom programmes is advocated.