The problem is that it isn't always clear how we should interpret a teaching portfolio, nor is it easy to sort out many of the portfolios I've seen.
So, the letter could say something like,
"As my enclosed teaching portfolio explains in detail, I have 3 years teaching experience, 2 of them at XX College the most diverse community college in the state. I also fulfil X, Y and Z stated requirement, as my CV and requested transcrips can verify" --
The thing is, the committees I've been on have worked very hard at writing an ad that actually states what we need to see from a candidate. Due to the number of applications, the initial review is very quick... if it isn't clear that you meet our minimum qualifications (and you'd be suprised at who thinks they can teach philosophy... ), and then if it isn't clear how you meet our preferred qualifications, we aren't going to go reading the tea leaves to figure it out.
The purpose of the letter is to give a hint as to why you are qualified -- and if the hint is "see page 4, paragraph 2" [i.e. of the teaching portfolio --PGS] -- that is sufficient.
[. . .]
When answering the diversity question, remember that there are a variety of ways it can be successfully negotiated... while still being a white male :).
1) I taught X population at my school.
2) I went to y school, which is very diverse
3) I cover a, b, c (religious, cultural, gender, age) diversity issues in my class
4) I have taught both older and younger students.
5) I have taught recent immigrants
6) I was an immigrant
7) My experience living abroad was...
8) I was a non-traditional student during x period.
9) I speak 3 languages
10) I was involved in X student activity/committee/public event, which was involved in diversity issues on my campus.
I'll be writing cover letters today and tomorrow and this is going to be a huge help. Inside the Philosophy Factory--massive thanks from me, and no doubt from others too.
Okay, now I have to get ready to hole up in the photocopy room and kill me some trees.