It is funny how all of the previous posts are from teachers new to the field and already they have hit on one of the biggest hurdles in teaching science- when is there time.
Here are some things to think about.
1) Link some of it to literacy/math. The NGSS does a remarkable job of outlining links to ELA and Math Standards on each Performance Expection. Use this as a bridge to steal time from the literacy block.
2) Scientists write and read. In fact many of our NGSS practices involve gathering information and communicating results. Yes, we want students doing the hands-on fun stuff, but developing multiple modalities where students can engage with the material is necessary to go deep into the topics. Reading informational text is also overlooked a lot in elementary. Science and Social Studies are perfect places to put those standards.
3) All disciplines have some form of Question- Evidence- Claim foundation. This is the basis of science lessons. We have something we want to solve, we gather evidence from experiments and experts, then we make a claim as to how we can answer that question. It is no different in social studies (except they are using primary and secondary sources instead of experiments). In ELA we often ask kids to give us text evidence after reading something, and in math we make them show their work as evidence.
4) Is teaching literacy the same as teaching someone to be literate? Think about that. Teaching someone to read letters on a page is only one step. To be literate they need background knowledge to link new information to when they encounter it. I think of K-2 as learning to read, and 3-5 as reading to learn. Science and social studies are perfect vehicles for this.
I hope this helps. Good luck!!