It sounds like enough to file an order to show cause and get mom into court to answer for it. If you're doing this without an attorney (if you walk into case management, they will probably be able to help), you'd want to seek temporary restraints consisting of suspending mom's parenting time on days that precede a school day and making this a permanent modification to the parenting schedule on the return date of the OSC (or referring you two to mediation to adjust the parenting schedule). Include - copy of prior orders, copy of letter from school.
Here's the form for an order to show cause. If at all possible, block and copy it into a word processor and modify it rather than printing it out and writing on it: http://www.judiciary.state.nj.us/civil/forms/10308_osc_temp_restrain.pdf
As always, this is general information, not legal advice - I encourage you to at least get a consult with a Family Law attorney in your area. I don't have a standard referral for Essex, but hunt around on Avvo, I'm sure there's someone local who can meet with you.
IF YOU LIKE THIS ANSWER AND APPRECIATE THE TIME IT TOOK TO WRITE IT, PLEASE SELECT IT AS "BEST ANSWER." Thanks. The above is said without seeing your case file and without my understanding the entirety of the facts of your case. Depending on those facts, the above information be may incomplete or may be completely inaccurate. The above is intended as general information only based on what you described and not as legal advice. I advise you to consult with counsel who may be able to provide better information commensurate with a better understanding of your situation.
From the facts provided above, it certainly seems that you have a basis for a Modification application. You may, in fact, have a basis for an emergent motion as Mr. Davis has suggested, but the Court generally does not treat parenting time matters as emergent. With that being said, the fact that your son is apparently in danger of suffering significant educational consequences may cause the Court to hear your matter on an emergent basis. I certainly recommend that you consult with an experienced Family Law attorney who can review all of the facts and circumstances involved in your matter and advise you accordingly. Please also take a look at the articles located at the link provided below for additional information. Best of luck to you and your son!
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I agree that from the facts you present a court will hear a motion for change in parenting time. Do attach the school notice to your motion.
973-984-0800. Please be advised my answers to questions does not constitute legal advise and you should not rely on it, due to the fact that we have never met, I have not been aprised of the facts in you case nor have I reviewed any documents.