This paper examines children's number fact knowledge in relation to mathematics problem solving. These findings are derived from a study that set out to explore the impact on mathematics learning of using multiplication and division contexts with 84 five- to seven-year-old children from diverse cultural and linguistic backgrounds. After a series of focused lessons, children's knowledge of number facts, including single-digit addition, subtraction, and doubles improved substantially. However, children did not always apply this knowledge to relevant problem-solving situations. The difficulty level for recalling number facts was not directly related to the magnitude of the numbers, with certain salient facts such as 5+5 and 10+10 learned earlier than facts with smaller sums such as 2+3 and 1+4.