What Exactly Gets Differentiated?
Content is what the student learns, process is how they practice it, and product is how they demonstrate it. You can offer a text at two reading levels, a hands-on activity alongside a written one, or let a student answer orally instead of in writing.
Keep the learning goal itself fixed for the whole class, and change only the path to reaching it - differentiation is not lowering the goal, it's varying the route.
How Do You Plan Without Tripling Your Workload?
Start from the lesson's core goal, then design two or three ready options for the parts most likely to create a barrier, instead of rewriting the entire lesson from scratch.
Reuse the same materials across levels with small adjustments - a shorter text, a visual aid, a worked example - and prepare these options in advance rather than improvising mid-lesson.
How Do You Know a Student Needs a Different Path?
Watch engagement, the type of errors, and how long a task takes. A student who finishes instantly and one who can't start both need a different path, just in opposite directions.
Don't assign the same student to the same option for every lesson automatically - re-check the fit regularly, since a need in one subject or topic doesn't necessarily apply to another.