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Affects social skills: It takes away quality time kids could otherwise spend with their family / neighbors. Time that would help them acquire these important skills, forge bonds.
Home assignments make students with internet access feel superior to students, who don't have access.
Given the attention span of kids these days in the classroom, it's good to have short projects that can be done over a week to re-visit some of the concepts
Often I see that more than kids parents do these projects. About attention span even if say this assumption is right, it's school's responsibility to work around it. So finally even short project, homework hardly achieves anything.
They are good opportunities for students to practise their skills in the course's specific area.
For instance programming assignments are the only way to learn programming properly.