This is supposed to be a mostly self-guided lab so students go through the full scientific method, while identifying variables.
Written instructions for students and a fill-in-the-blank lab report are provided. Rubrics are provided. The first focuses on testing each part of the instructions' details. The second focuses on student performance. The last focuses on ease of grading. A 'key' is provided that is simply a sample lab report. I suggest providing it to the students if they are new to lab reports.
This was written for middle school students, but I'm sure it carries over to high school. For high school, I would add a section for identifying error and improving the experiment at the end.
This is great for a substitute assignment since it is self-guided and engaging. Students perform the experiment and fill in data when the teacher returns.