Teachers: do you agree with Malcolm Gladwell that class sizes below 25 are TOO small?

The podcast/interview from last week with Gladwell is here; at 27 minutes in, he explains why he thinks classes can be too small:
“I got this idea from teachers, I spoke to countless teachers...I found it hard to find, particularly middle and high schools teachers, who thought that it was a good idea to have a class in the mid-teens….When a class gets too small it hurts the poorest students.”I have never heard any teacher say this myself and don't know any research to back it up. In any case, Lehrer doesn’t want to hear from me, but from teachers to express their