[gus_massa]

I agree. My older daughter was learning to read before school, and we started with the usual here in Argentina:

  ma, me, mi, mo, mu
  pa, pe, pi, po, pu
  sa, se, si, so, su
  ...

after a few more rows, we expected her to generalize because she is very smart, but it's harder than what we expected and we have to told her all the 21x5 cases. (The first cases were harder, and the lasts got easier.). I don't remember about the longer silabes like "pra", "bla", ... and there are weird words like "consternado" but I guess it was not obvious.

[tuukkah]

Yes, I think it will be somewhat random how many cases each child needs to be taught before they generalize. One thing I forgot to mention is that for polysyllabic words, they use a learning aid here: in the beginning, the syllable boundaries are marked with dashes in all text and in the second year, only in longer words. I don't know if it works in Spanish too, something like this: "A-yer ce-na-mos cons-ter-na-dos." Again, I think it's unnecessary for some children but helps others to keep learning while gaining more experience with the syllables.