A new Malmquist-type index to analyze two or more groups of DMU when only a pseudo-panel database is available.

Extends Camanho and Dyson's one-period Malmquist-type index approach.

This new index is useful for comparing schools using databases like PISA or TIMSS.

We provide a comparison between public and private school performance in the Basque Country.

Results show that private schools outperform the public ones.