The study, which is derived from a larger study, compares grades 10 – 12 mathematics learners’ non-routine problem solving. An exploratory study was conducted on a convenience sample drawn from three high performing high schools located in Tshwane North District, Gauteng province of South Africa.Learners wrote a non-routine problem solving test. Findings revealed that the 11th grade learners obtained the highest mean score while that of the 10th grade learners was the lowest. High school learners’ level of strategy use on solving non-routine problems improved significantly as they progress from grade 10 to higher grades. No significant difference was discovered as learners progress from grade 11 to 12.