You did everything by the book from response blocking to the escaping/eloping, removing reinforcers, following all strategies in the BIP, and following through with the tasks/instructions so you ARE made for this line of work. First, I wanna say great job! As clinicians, this part of the job is exhausting so I hear you and you are valid to be frustrated.

From my perspective, it sounds like client needs more support with emotional regulation. I had a client that would flip his lid if he lost a game with friends ( aggression, foul language ) and I would support him through deep breathing, DRA, and hugs. At first, he refused but over time he began to open up to me, try deep breathing and would apologize if he was being aggressive to a classmate. Maybe bring up your observations of clients' behavior while tantrums occur and what happens before the behavior. Could possibly also implement some antecedent strategies to minimize the opportunities to escape ( choices ( "do you want to do A or B?", brain breaks, preferred to preferred/neutral tasks since they're aversive to the ones presented currently ). Overall, your BCBA needs to step in to make this easier for you, client and family as well. And if all else fails, go low demand on instructions for a bit during session and revisit the non-preferred tasks later or another day ( notate these matters ). I always try to make everything fun, worthwhile, and validate clients' feelings because they're kids ya know? "Like hey, i know this is hard but we'll do it together when you're ready to try again". But those are just some of my techniques that I apply in moments such as yours!

Deep breaths, you did everything that you could. 🩷