In this task, you are given a question and a context passage. You have to answer the question based on the given passage.
Q: What did authorities use to decide which students went to which type of institution?, Context: The largest expansion of comprehensive schools in 1965 resulted from a policy decision taken in 1965 by Anthony Crosland, Secretary of State for Education in the 1964–1970 Labour government. The policy decision was implemented by Circular 10/65, an instruction to local education authorities to plan for conversion. Students sat the 11+ examination in their last year of primary education and were sent to one of a secondary modern, secondary technical or grammar school depending on their perceived ability. Secondary technical schools were never widely implemented and for 20 years there was a virtual bipartite system which saw fierce competition for the available grammar school places, which varied between 15% and 25% of total secondary places, depending on location.[citation needed]
A:
their perceived ability