How can a maths teacher be so bad at budgeting?

[Peppermintee]

My DH teaches Maths.
He oversees out bills account, I oversee our extras/savings account.
I asked him how things were adding up in our bills account after receiving a text from the bank saying there wasn't enough money in there to cover the month's bills. He said there "should" have been enough and transferred some money over from our extras account to cover it.
Then did nothing.
I pressed that the account needed looking at. He said it had just been a busy month.
I then accessed the account and all out statements. We have been underpaying in the account for 9 months by £150, putting us in our over-draft after having a cushion of 1000 in there 1 year ago.
He says "sorry."
I don't get it.
Why can't a maths teacher budget?
Any tips for budgeting better? I think I need to oversee all our finances now, but can't believe this is the case. He is offended when I say I am going to oversee things from now on!

Well, on your list, we have-
100 Xmas
100 kids (clothes, shoes, school trips, classes and clubs)
100 household maintenance (inc diy)
150 "special" travel (won't stretch to holidays with accommodation but gets us on visits to distant family and friends)

We each have 130 personal money (including all clothing, hair, gym, meals out and doing extravagant things with the kids because we want to)

It sounds like we are fairly close to you in means.
We've been using YNAB for long enough that we've winkled our all our annual expenses and put money by for those.