Do you want your class to learn about the language of explanation whilst also learning how to host parties and start fires in the wild? Try the dice activity 'Cause and effect'.
I can use causal connectives to extend a sentence or begin a new sentence.
When writing explanations, many children find it difficult to discern between conjunctions that join sentences (eg because, so) and adverbs/adverbials that begin a new, closely related sentence or at the very least follow a semi-colon (eg however, as a result of).
This activity gives children lots of opportunities to use causal connectives (because, so, so that, however, consequently, this means, this will, this may, as a result of this) orally and in sentences. Most importantly, it helps them to think about whether they are extending a sentence or beginning a new one.
This could be used before my other popular resource for explanation writing: 'Explain yourself'. That activity enables children to develop a full explanation, whereas this narrows the focus to sentence skills.