Sydney's Catholic schools will have selective entrance tests for the first time this year, with high schools across the diocese to offer places in selective streams for gifted and talented students.

In a bid to stretch their brightest students and stop a drift to high-achieving public selective schools, Sydney Catholic Schools has been developing an external selection test with the Australian Council for Educational Research, which year 6 students will be able to sit in term three this year.

But unlike admission to the state's highly competitive selective schools, students will not be offered a place based on their test results alone.

Instead, gifted students will also be required to submit a portfolio, which could include samples of their class work, reports and a recommendation from their primary school principal.