DS (6.1, ASD) has been learning to read for the last 2/3 months and is doing very well with sight words. He is also doing headsprout and starfall and is beginning to blend words every now and then. Words that he have learnt as sight words he knows very well and makes no mistake on them. But it's been really puzzling why sometimes if I show him a new word he can read it without any prompt, sometimes he just can't. Any ideas?