Extra payments to be made?

My wife and I signed a Separation Agreement around 6 months ago. We sold our home, where she took a slightly larger percentage of the equity and bought a flat outright. I am currently renting. We both have our own businesses and our salaries are similar.
We have 2 children (12 & 9) and nearly equal childcare. During term time childcare is 6 nights me /8 nights her, out of every 14 nights. During school holidays we share equally, week on-week off. Essentially this means 169 nights pa with me (just short of the 175 which the CSA calculator puts into the top band!)
I agreed £230 pcm (based on CSA calculator) plus half of school trips. I buy clothes to keep at mine of course, and obviously my housing needs are exactly the same. We each make lunches or provide cash to buy them.

I''m now being asked for half of a drama club fee for both children. It''s not about after-school care as they go on different days - sometimes mine, sometimes hers.
It''s only £150 for the term but I don''t want to set a precedent if it''s not fair. So, that''s my question - is it fair? I think I''m already paying my half in the form of CM.
In the past, when I''ve asked what she thinks CM should be for, she has replied that she doesn''t have to justify it - correct I guess, but not helpful.
I know I could technically just refuse as it''s not in the agreement. However, I don''t want the girls getting the impression that I''m being mean. Plus, I genuinely want to know what everyone thinks - fair or not?

Well under CS rules you have already given more than you have to by providing for school trips etc.

Does she get any tax credits? Presumably she also claims the CB? how much extra is she getting?

Other things to consider is can you afford it? If you say yes to this what will it be next?

There will have to come a point where you have to say no but at 12 and 9 the children shouldn''t be included in the conversations.

Thanks for your reply.

Yes, I can afford it, but...so can she.
She is mortgage-free and works very similar hours to me. She does also receive family tax credits (I presume) and CB.

I don''t want to fall out over it, as the childcare arrangements have worked well thus far. However, I also don''t want this to be the thin end of the wedge and to be taken advantage of. Ultimately, I just want it to be fair.

Any other opinions?

In my opinion you have summed it up yourself. You can afford it and don''t want to fall out over it as everything is amicable and works well which is priceless.

You could tell her this is the last thing and you wont contribute to anything else or how about giving her a taste of her own medicine and arrange an activity and ask her for half the cost?