Learn Turkish: Biz aynı sınıftayız. - We are in the same class.

This is because of consonant assimilation. The suffix for 'in' or 'at' is usually -da or -de. However, the word sınıf ends in f, which is a voiceless consonant. In Turkish, when a suffix starting with d attaches to a voiceless consonant, the d changes to a t to make it easier to pronounce. So, sınıf + da becomes sınıfta.

What is the purpose of the -y- in sınıftayız?

The -y- acts as a buffer letter. In Turkish, you generally cannot have two vowels right next to each other. When we add the personal suffix -ız to sınıfta, we get two vowels side-by-side (a and ı). The -y- steps in to separate them, giving us sınıftayız.

How do we say the 'are' part of 'we are' in this sentence?

It is built right into the end of the word! The suffix -ız is the personal ending for 'we'. When attached to a location like sınıfta, it translates to 'we are in the class'.

Could I drop the word biz and just say Aynı sınıftayız?