The resolution is ambiguous because Ali's experience in the movie is mirrored in his father's (larger) experience. Like Ali who spends the entire movie lacking and unable to provide for his sister's shoes, his father walks a similar path, unable to provide for his family, despite his best efforts to pay the rent, take care of his wife etc.Like Ali his father uses his body to try to fulfill his duty.This isn't just a kid's movie and while Ali's troubles are the center of the movie it's not the message. The basic message is one of hopefulness. The shoes represent not only Ali's fulfilling of his efforts but his father's ability to provide for his family as well. The reason it's ambiguous is so that the father doesnt' get all the credit at the expense of Ali.They have both done their best and both are "heroes" in the movie.

SPOILER...
But It had the perfect ending! The kid thought he failed his sister but Dad was on his way home with a pair of brand new shoes for both kids... Kid became the school hero ( surely bringing much pride to parents as well) and Dad had the opportunity to be the hero and bring much joy and happiness!