We only teach 18 or so, and honestly I don't think it's enough. But it's rare that I have a child that doesn't know them all by the end! We expect them to read them, and if they use them in their writing assessments we expect them to be spelled correctly by the end of the year.
At my old school they were given 100 sight words, with the hopes that they would know half of them by the end of the year.
I love how I teach sight words. It's hard to explain, but I'll try.
I start with a sentence frame, and have each child dictate a sentence to me. I write each sentence on chart paper and they "help" by spelling the words, reminding me to use spaces, helping me sound out new words, use punctuation, etc. We do this over the course of 2-3 days. Then when all of the sentences are done the kids get to come up and use a pointer to lead the class in reading their sentence. They read it first and then the class choral reads. The last day I cut the sentences up. Each child has to put their sentence back together, glue it down, and illustrate it. We then make these into class books (which are their very favorites to read!).
Doing this not only hits on reading and writing the sight words, but on alphabet and sounds, segmenting, writing conventions, sentence structure, etc. I feel like it is one of the most valuable things we do.