Written with people moving from Turkey in mind. The Portuguese rules still apply more broadly.
Public Schools: Language Barrier
Public schools are free, but the curriculum is 100% in Portuguese. There are no "English public schools." For young children (under 6), immersion works well. For teenagers, it can be traumatic and lead to losing a year.
Schools offer "Português Língua Não Materna" support classes, but if your child is older and doesn't speak the language, you should budget for a private international school.