Why do most phonics programs start with short a? Why not one of the other vowels?
I dont know for sure, but I suspect it is due to simplicity. Short <a> is the simplest vowel sound to spell, because it has only two spellings: <a> as in act
and <au> as in laugh
and one pronunciation of aunt
. Short <e> has seven spellings, as in any, said, says, met, head, leopard, friend
. Short <i> has twelve, as in chocolate, bargain, closet, been, foreign, hit, carriage, mischief, women, busy, build, crystal
. Short <o> is complicated because in elementary treatments it often collapses three similar, not easily discriminated sounds, those in block, father, caught
. Those three sounds have sixteen different spellings. The idea of short <u> often covers two similar sounds, as in cut
, with twelve different spellings. So it is probably easier when teaching beginning spellers, to start with the simplest, most regular and predictable spellings.
For more on these sounds and their spellings, you can go to the Correspondences: Sounds to Spellings table in the CommonWords database elsewhere on this site.