Thank you for the many contributions you sent in. Many pupils also wrote about how they did the counting and others just sent in the total number, which was $23$. Charlotte also S Anselm's Prep School, sent a rather different way, together with a picture to illustrate it.

I put little rings around the dots like you would in a wordsearch. Then I counted up how many dots were in each ring remembering not to count the ones we've already counted! I did the sums by the side to add up all the dots in the rings (which I called carniverous worms) and it came to ... $23$.
Thank you all of you and for the splendid solutions from S. Anselm's. Keep the solutions coming in.