Ten books introducing alternative vowel spellings.
Book 1: ay, ai, a, a-e, ea, ey
Book 2: ee, ea, y, e, ie, e-e, ei
Book 3: ow, oa, o, oe, o-e
Book 4: er, ir, ur, or, ear
Book 5: ow, ou & oi, oy
Book 6: oo, ue, u-e, ew, ou, u
Book 7: igh, ie, i-e, i, y
Book 8: aw, awe, a, au, al, ough
Book 9: air, are, ear, ere, eir
Book 10: ar