Performance of candidates in Kenya Certificate of Secondary Education Mathematics in Meru County of Kenya from 2012 to 2016 has consistently been deteriorating. This has called for this study so as to establish whether this trend has anything to do with organization or otherwise of external Mathematics contests in secondary schools of Meru County of Kenya. The study adopted ex post facto design because the effects of independent variable on dependent variable had already occurred. Research instruments were Mathematics teachers’ questionnaire, and Principals’ interview guide. The target population was 299 principals and 836 Mathematics teachers in the County. This study used stratified random sampling with proportional allocation. The sample size was 30% of the total target population. It was established that most principals did not organize Mathematics contests, to the detriment of performance of their KCSE candidates.