An assessment of internal efficiency allows policymakers and education administrators to understand how cost-effective the desired educational outputs, such as promotion and retention rates of students, are being produced from a given input. In Macau, where private school enrollment accounts for more than 90% of the total K-12 student enrollment, this study attempted to explore if a private-sector-dominated school system can be equally efficient in basic education. The internal efficiency was estimated for each educational cycle from 1996 to 2003 based on the reconstructed cohort method. The results of this study revealed that, on a seven-year average, the highest coefficient of efficiency was attained in preprimary education (99%), followed by primary education (90%), and then by upper secondary education (85%). Lower secondary education was found least efficient among four cycles, averaging only 79%. The years-input per preprimary, primary, lower and upper secondary graduate were 3.03, 6.67, 3.79, and 3.53 respectively. The wastage of educational resources was found worse in secondary education as the input-output ratios revealed that an additional 26% and 18% of the ideal resources were required to produce a lower and upper secondary graduate respectively.