When I taught Key Stage 2 French, my favourite way of introducing and practising grammatical gender was using the book un triangle by Néjib. You can read about the book and what I did with it here.
With my Year 5s I've just started Unit 13 of my scheme of work for Key Stage 2 Spanish, which is all about description.
We started off by reading the poem Redondo (Round) by Gloria Fuertes, and talking about why the adjective is spelled in three different ways.
Then I showed the class the Spanish words for ten more round things. We gave out the Spanish dictionaries, and the children worked in pairs to look up the new words, find out if they were masculine or feminine, and decide whether we would need redondo or redonda to describe them.
We put the answers in the form of a new poem inspired by the one by Gloria Fuertes.
While we were working on this activity, I had an idea inspired by un triangle and its family of books. The next week, I introduced the class to the adjective cuadrado, which they had first met in Year 2.
I gave them the challenge of finding in the dictionary the Spanish words for things that are square and putting them into a line of poetry following the example above, and working out whether they would need the masculine or feminine form of the adjective. The children worked in pairs on their poems and used this guide to help them. I also showed them the book un carré by Néjib, to show them how the thing didn't have to be something square exactly, but something that had a square as a part of it.
The following week the children copied up and illustrated their excellent poems, and I now have the difficult task of working out which ones to put forward for the next issue of Write Away! next month. Here's one of them as an example of the poems the children created.