I have been retired for about a decade, and I homeschool.
It would not be grounds for removal in and of itself. The social worker could be 'loading up' the petition. It will be one of the issues that will have to be discussed and resolved (through agreement by all parties) in court, with all of the parties coming up with a plan to address the deficits. This could include homeschooling with the assistance of online resources.
The key is going to be the parents' counsel (whether court-appointed or not)(the attorneys). The fact is that parents have a legal right to homeschool. No matter what a know-it-all says, it can be done in a very effective way very easily, particularly in light of the online resources available. The parents need to stick to their guns, so-to-speak, and propose a plan that addresses any issues that come up.
As we all know, many, many kids in conventional classrooms are behind or 'below grade level.' It simply cannot be guaranteed that the children in question would have done better in a conventional classroom; that's just a guess.
There is a great deal of prejudice against homeschooling within the social worker and education communities. I have been able to educate many friends still in the profession about the benefits.
As a precaution, I go through a public charter school, operated by a public school district (and this could be a compromise that would work for those parents). Technically, what we are doing is called 'homestudy.' We meet with a teacher monthly, and keep up an appropriate plan, in addition to using conventional books and materials.
Additionally, I completed law school (juris doctor) after I retired. I do not, myself, give legal advice. I have the number of one of the best parents' attorneys in the state on speed-dial. I have copies of the legislation in my state that authorizes homeschooling. A judge who attacked homeschooling in one of his rulings (technically an appeals court justice) in my state was slapped down by our governor and legislature, who stated that his ruling only applied to one dependency case (and the full court supported that later), and that they would legislate as necessary to support homeschooling.
Lord help anyone who attacks my homeschooling, because I am prepared to make the argument of a lifetime, and I will take it as high as necessary (I have the funds). I have always supported parents' rights to make these vital decisions, and screw the holier-than-thou, sanctimonious know-it-alls and foes of homeschooling. I know our legal rights and will not be bullied. The parents' attorneys need to contact the HSLDA (the Homeschool Legal Defense Association). Their attorneys-at-law are expert in these issues.
http://www.hslda.org/http://www.hslda.org/about/staff/attorneys/Smith.asphttp://www.hslda.org/about/staff/attorneys/Jones.asphttp://www.hslda.org/about/staff/attorneys/Schmidt.asp