former fc supervisor here and no offense taken-there ARE some lousy social workers out there just as there are great ones.
i'de suggest you find out first how the agency (differs allot from state to state, county to county, and if it's a private agency) operates it's fc program so you can learn whose responsible for what. in the one i worked in (a county gov. agency) each child had a minimum of 2 staff members assigned to them. there was the "social worker" who handled the home visits, the court appointments and providing "services" (transportation, authorizing one time or special items of need, reunificiation...). then there was the "eligibility specialist" who determined and maintained the child's eligibility to the financialy based items (the monthly foster care payment, food stamps-if eligible, medical coverage, special intermitanat funds-like a clothing payment, camperships...). once you find that out you will know who to address with your concerns (or whose supervisor to contact).
i'm guessing the agency the child is under knew where he was at (were you receiving his monthly payment? receiving any letters?). as far as school goes-not sure how it works where you are but in many areas the schools are provided with a form at the begining of every school year (or at the time of enrollment) for every child receiving fostercare (or public assistance) that identifies their link to social services-if the child's attendance drops to a certain level or disenrollment occurs then social services is notified. if school's been an issue before with the child then it could go a step further with the counselor having some kind of reporting relationship with the social worker. as for the child having no family-were you told this by the placement worker? it's rare that a foster child has no family at all. the goal of foster care is family reunification and the majority of kids in foster care are there because someone (usualy one of the bio parents) has had the child involuntarily taken away from them but full blown parental rights have'nt been permanantly severed by the courts (there is a very small population though who have finished the court process but because of an extenuating circumstance like a very costly medical or special needs issue it's to the child's benefit to keep them under the umbrella of foster care so they stay eligible to the government paying for these-but in those cases it's usualy told up front to the foster parent because the placement ideal is one that would mirror adoption-the longest term placement as possible). if no kind of visitation is going on you want to find out what the child's status is-is the parent (or whomever the child was taken from) in some form of reunification plan-when can you expect visitation to be attempted? is this a voluntary or involuntary fc placement? (could it be that a parent was incarcerated and initialy placed the child with a relative who later voluntarily placed the child-in which case it could be that upon release of the parent absent any kind of pre-existing child welfare issues the child could be immediatly returned to them). this is all information i believe a fc parent needs to be aware of.
one of your best resources can be a fc parent support group in your area. those folks will know the in's and outs of the agency you work with (better than some of the staff who might only know what their individual function within that agency is). they can be a wealth of information and tremendously supportive (they can clue you in if you've got a "clunker"

of a social worker and who the most effective person within your agency to address it is). they can also clue you in on advocates who might be able to help you if the problems you are experiencing is unfortunatly the norm within your agency or state (some states have gotten heavily sanctioned by the feds but still plod along doing the same poor work, some states have sw's that are so over assigned the sad reality is until a horrendous tragedy occurs that brings a gloria allred or nancy grace publicly down on them nothing gets done).
kudos to you on being a foster parent-i tremendously admire people who go into this for the right reasons. right now school is out and it's not the rush before school starts so you might use it as an opportunity to contact your sw (or his/her sup) to find out what you need to best help this child, find out what their placement plan is, what the minimum oversight you should expect is. if they hedge or ignore you go to the next level (usualy a division manager) or up higher (a deputy or full bore director). if the agency you are with is government and you don't get satisfaction internaly you can step it up higher-board of supervisors, local governement rep. i have to say that one of the most effective meetings i ever attended was one where despite myself and my manager voicing complaints over the way things were being done with a particular population and it falling on deaf ears i encouraged several fc parents to complain up the ladder. a person on a high rung outside our agency finaly took note and forced the issue which led to accountability and action that was long overdue.
best of luck.