“When will she move up?” is the question every swim-school desk hears, and “soon” is the answer that loses families. Skills remaining, divided by how fast this student actually masters them, divided by lessons a week, is a date you can defend.
Nine skills left at 0.75 skills a lesson, once a week, is twelve weeks — a real answer, and one a parent can plan around.
The example
Three students in different levels, each with their own checklist gap, mastery rate, and lesson frequency.
| A | B | C | D | E | |
|---|---|---|---|---|---|
| 1 | Student | Skills left | Skills/lesson | Lessons/week | Weeks |
| 2 | Mia — Level 3 | 9 | 0.75 | 1 | 12 |
| 3 | Owen — Level 2 | 5 | 0.5 | 2 | 5 |
| 4 | Zoe — Level 4 | 11 | 0.6 | 1 | 19 |
The formula
Two divisions, each converting one unit into the next:
How it works
Follow the units:
B2is skills still outstanding on the level checklist — a count you already keep if instructors mark the card each week./C2converts skills into lessons. A rate below 1 is normal: most students do not tick a new skill every single lesson, and a rate of 0.75 means three skills every four lessons./D2converts lessons into weeks. Twice-weekly students genuinely do progress in half the time, which is the strongest argument for a second lesson you will ever make.ROUNDUP(...,0)because levels change on a lesson boundary. Eleven and a half weeks means the twelfth week.
Recompute after each session and show the parent the trend. A number that shrinks every month builds far more trust than a promise.
Try it: interactive demo
Enter the skills still to master, the student's mastery rate, and lessons per week.
Variations
Show the target date
Add the weeks to today for a date the front desk can say out loud.
What a second weekly lesson buys
Compare the two timelines side by side to make the case.
Pitfalls & errors
The mastery rate is per student, not per level. Averaging it across a class hides exactly the students who need a conversation.
Recalculate the rate from the last eight weeks rather than the whole enrolment. Progress is rarely linear, and a student who has just clicked deserves the newer number.
Do not present this as a guarantee. Frame it as “on current pace” — a missed month of lessons or a growth spurt changes the input, not the honesty of the formula.
Practice workbook
Frequently asked questions
How do I measure skills per lesson?
What about students who plateau?
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