Great! It was easy enough to find something on birthdays. I had a quick look in one of my resource books and found an activity that would work well with a class this size.
I started off by eliciting the months of the year, and then the seasons, asking which months were in each season. This was revision, but I really had little idea of what the other class had covered before the lesson. They all knew the months, if some of them had a few pronunciation problems. We then looked at how to say dates, which is normally a source of confusion for Spanish kids, since in Spanish cardinal numbers are used. We went through ordinal numbers and there didn't seem to be any serious problems.
We played a quick game of "Guess my birthday" with "hot and cold" clues to practise dates.
I then wrote on the board:
Somebody whose birthday is in the same month as mine.
in a month that begins with J.
This was to prepare the children for the following activity, where these kinds of sentences would appear on cards with presents.
I then told them all that they would each have three presents that they would have to give to other students.
I demonstrated by taking a card (I had very briefly cut up the cards whilst practising dates earlier- multi-tasking!) and reading it aloud. It said "Somebody whose birthday is in winter". I went round the class asking several individuals when there birthday was until I found somebody whose birthday was in January. I then repeated with a different card. After that, I asked the class what question they had to ask the other students (to see if they had been paying attention and to make sure they all knew what they had to ask).
I gave out three cards to each student. And then came the mingle! Fifteen eight to ten year olds actually successfully managed to complete the task (mostly!) in English. After this task, we discussed who had received the most presents and why (because their birthday was in a month that began with J and was in summer etc).
We then all sang Happy Birthday to Jorge, asked him what (real) presents he had got and the did a quick pairwork activity talking about the best present you would like to get.
The activity I did was from Speaking Activities (Junior English Timesavers) by Cheryl Pelteret and Viv Lambert, Scholastic. However, you could make your own similar cards using language that your learners are capable of understanding. You could make the clues more simple or more difficult.
This is yet another example of how improvisation can work in almost any situation, even when you don't know the learners. As long as you do something that interests and engages the students (and hopefully teaches or practises some language) the lesson should work.
Note: I actually learnt some silly versions of the Spanish version of Happy Birthday, Cumpleaños Feliz in this lesson. Does anybody remember any English versions? There was one that went: Happy Birthday to you, squashed tomatoes and stew... but I can't remember the rest. These could be fun examples of authentic (if nonsense!) English rhymes and I can guarantee the kids will love them!