What a worksheet is good at
A worksheet does one thing well: it provides structured, repeatable rehearsal of something a child already understands, in a form that can be done independently and checked afterwards.
That is genuinely valuable. Fluency requires repetition, repetition requires material, and producing that material by hand for every child is not a realistic use of anyone's time. For consolidating a method, building recall of facts, and finding out what has stuck, paper practice is hard to beat.
It is also honest about what a child can do alone — which is different from what they can do with an adult prompting at their shoulder, and often more useful to know.
Introducing a concept is a different job
The most common misuse is handing out a sheet to teach something new. A worksheet cannot explain, cannot notice confusion, and cannot respond. A child who does not understand the first question will either guess their way down the page or stop, and both outcomes waste the sheet.
Worse, guessing consistently produces a wrong method applied thirty times, which then has to be unlearned. It is entirely possible for a practice sheet to leave a child further from understanding than before they started.
Teach first, by whatever means suits — talk, objects, demonstration, a whiteboard — and check the child can do two or three examples with you. Then print something.
Skills that need objects, not paper
Early counting is the clearest case. One-to-one correspondence — one number word per object — is about moving things and touching them. A picture of six apples cannot be pushed into two groups of three, and the pushing is where the understanding comes from.
Fractions have the same character. A child who colours in three quarters of a shape on a worksheet may be following an instruction about colouring rather than thinking about quantity. Cutting something and sharing it makes the idea real in a way the sheet assumes has already happened.
Place value, likewise, is best met with objects that can be exchanged — ten of these become one of those — before it is met as columns on a page. Column arithmetic is a notation for something; teaching the notation first tends to produce fluent procedure over an empty space where the concept should be.
Things worksheets cannot assess
Reasoning is largely invisible on a worksheet. A correct answer might come from understanding, from a half-remembered rule, or from a lucky guess, and the page cannot distinguish them. Asking a child to explain one answer out loud tells you more than the other nineteen ticks.
Speaking and listening obviously cannot be assessed on paper at all, which sounds too obvious to say until you notice how much of a typical week is paper-based.
Reading comprehension sits somewhere in between. A worksheet can test whether a child retrieved a detail from a text; it is much weaker at whether they understood it, and weaker still at whether they enjoyed it — which for a developing reader may be the thing that matters most.
The compliance signal
There is a recognisable state where a child is completing worksheets neatly, on time, with reasonable accuracy, and learning very little. The work is done because it was set. Nothing is being extended.
Two signs are worth watching for. One is uniform accuracy — a child who scores nearly full marks on everything is being given work below their level, and the sheets are measuring compliance. The other is a child who finishes quickly and shows no interest in what the answers meant.
The response is not more worksheets and not fewer, but harder ones: raise the level until mistakes appear again. Around 80% accuracy is a reasonable target for practice material. Full marks every time means the sheet has stopped doing anything.
A short checklist before printing
Has this been taught, and can the child do two examples with support? If not, teach it first.
Is the skill something that lives on paper, or something that lives in objects and talk? If the latter, the sheet is a record of the learning rather than the learning.
Would I be able to tell, from the finished page, what the child understood? If the answer is no, add a question that asks them to explain one answer.
Is this the right length for this child, or the length that fills the page? Those are rarely the same number.