we do everyday homework horizontally, however every week we have a "big one" 手紙、話 and we are given pages for vertical writing. i always forget where to place dots and ゃ っ and all the rest
and that handwriting is ok. hirigana can't be messed up easily to a point you can't make it out.
however i do not like handwriting of kanji when my teacher (japanese native) or any tourist at my shop does it. they often draw them without lifting the pen up so some parts seems "jointed" and for me, who writes them as in books, it is hard to make out.