"你是第几个到教室的"用英语怎么说?

ARE YOU BELONG TO
那个老师教你的？
笑死人
potoby 的答案不错虽然比较复杂

“第几个”没有一个直接对应的英文词. 翻译时应灵活处理.
林肯是美国第几任总统？
Which term of US President did Lincoln serve as?

那是你们开的第几家店？
Is that the first store you opened?
When did you open that store among all your stores?

我不记得这是我第几次来圆明园了.
I could not remember how many times I have visited Yuan Ming Yuan/The Old Summer Palace/the Gardens of Perfect Clarity.

洛迪丝是麦当娜的第几个女儿?
Is Lourdes Madonna's oldest/youngest daughter?

你在家排行第几?
Are you the oldest/youngest child in your family?

参考资料：
http://art.kaola.cn/u/watt/89579.html
http://thetonyshome.blog.sohu.com/59255009.html

Which sequence are you belong to entering the classroom？这个是正确的说法，我保证。

how many students were there in the classroom when you came into classroom?

或者复杂点问 “ did you the first one arrive at the classroom?"

试下，看管用不？

How many students arrived at the classroom earlier than you did?

Which classroom are you in?