ATAR scaling, in plain English

What scaling actually is

Scaling is the adjustment that lets the system compare a 75 in Methods with a 75 in Psychology. Without it, students who chose easier subjects would always finish above students who chose harder ones, and universities would have no fair way to rank applicants. With it, your raw mark gets pushed up, down, or held roughly flat, depending on how strong the cohort sitting next to you was.

In WA, scaling is a joint exercise between two organisations. SCSA (the School Curriculum and Standards Authority) sets the syllabus, runs the external exams, marks them, and produces your school-assessed marks and your raw exam marks. TISC (the Tertiary Institutions Service Centre) then takes the standardised combined marks for every ATAR course and applies the scaling algorithm. The official policy and methodology sit with the joint TISC/SCSA Scaling Committee.

The algorithm TISC uses is called Average Marks Scaling, or AMS. The headline rule of AMS: each course is adjusted so that the average scaled score in that course matches the average scaled score that the same students earn across all of their other ATAR courses. If the Engineering Studies cohort, as a group, performs better across all of their courses than the Accounting cohort, Engineering Studies marks get pushed up relative to Accounting. It is a statistical adjustment for cohort strength, not a judgement on the subject itself.

The seven steps from raw mark to scaled score

This is the actual TISC marks-adjustment process. Every ATAR course in every school in WA goes through these steps every year:

Typical scaling pattern in WACE

Exact numbers move a little each year (TISC publishes them annually). The rough shape below has been stable for years:

Subject	Direction	Rough magnitude
Mathematics Specialist	Scales up	Strongest scaler in WA
Mathematics Methods	Scales up	Strong
Chemistry	Scales up	Moderate
Physics	Scales up	Moderate
Literature (English Lit)	Scales up	Mild, smaller, stronger cohort
English	Roughly flat	Big cohort, near average
Biology	Roughly flat	Slightly down most years
Human Biology	Roughly flat	Slightly down most years
Mathematics Applications	Scales down	Mild to moderate
Psychology	Scales down	Mild to moderate, large mixed cohort

Source pattern: TISC's annual scaling reports (tisc.edu.au). Always check the latest year's numbers before making decisions.

The maths rule everyone gets wrong

WA has three ATAR maths courses in increasing difficulty: Mathematics Applications, Mathematics Methods, and Mathematics Specialist. They don't all combine cleanly when TISC builds your ATAR.

• Applications + Specialist is an "unacceptable combination." If you sat both, only the higher of the two scaled scores can count toward your aggregate.
• If you sat all three maths courses, only two can ever count toward your aggregate. You can keep Methods + Specialist, or Applications + Methods — but never Applications + Specialist.
• Methods and Specialist also each give a 10% bonus on top of their scaled score (more on this below).

From scaled scores to your ATAR

The scaled scores feed into a Tertiary Entrance Aggregate, or TEA. TISC's formula for school leavers:

TEA = best 4 scaled scores + 10% of best LOTE + 10% of Methods + 10% of Specialist

No course can count more than once. Subject to the unacceptable-combination rules above. Maximum possible TEA is 430.

Here is the TISC worked example, exactly as published in their marks-adjustment paper:

ATAR subject	Scaled score
Physics	89.90
Mathematics Applications	87.55
Mathematics Methods	85.00
Mathematics Specialist (excluded: unacceptable with Apps)	84.00
English	78.90
Economics (not in best 4)	77.85
Sub-total of best 4	341.35
+ 10% bonus on Methods	8.50
+ 10% bonus on Specialist	8.40
Tertiary Entrance Aggregate (TEA)	358.15

The TEA gives you a ranking inside the ATAR-eligible candidature. Your ATAR then ranks that candidature against the entire Year 12 school-leaving age cohort (16-, 17-, 18- and 19-year-olds in WA, weighted by ABS data; 20-year-olds count zero in WA).

The mapping from TEA to ATAR uses a cubic spline participation function, the model proposed by Harrison and Hyndman in 2015 and adopted by every Australian Tertiary Admissions Centre (ACTAC) from 2016 onward. The output is an ATAR between 0 and 99.95 in steps of 0.05. An ATAR of 80 means you sit at the 80^th percentile of the Year 12 school-leaving age cohort.

How to use this when picking subjects

The temptation is to pick whatever scales hardest and grind through it. That is usually a mistake. Scaling rewards strong students in strong cohorts: if you'd be a struggling Methods student, the scaled score you get from a 50 in Methods is often lower than the scaled score you'd get from an 80 in Applications. AMS helps high performers; it does not save mid performers from a subject they hate.

The TISC FAQ puts it bluntly: "Choosing courses on the basis that they are usually scaled up may actually result in a lower scaled score than you might have otherwise achieved."

The better rule of thumb:

• Pick subjects you can perform in the top half of the cohort, with effort.
• Among those, lean toward subjects that scale up, because the same percentile gives a higher scaled score.
• If you're aiming above 95, you almost always need at least one or two scaling subjects in your top four: Methods, Specialist, Chem or Physics.
• Methods + Specialist together are uniquely powerful: two strong scalers plus two 10% bonuses on top.

How to use it when planning study time

Once subjects are locked in, study time should follow marks, not interest. Five hours invested in your weakest scaling subject usually moves your ATAR more than five hours invested in your strongest non-scaling subject, because percentile shifts have larger effects in scaling subjects. The flip side: don't neglect the subject you love just because it scales flat. Top scores in flat subjects still pull a top-four ATAR up.

This is exactly the kind of conversation we have with every Educatta student in their term-one planning session. It is also the conversation most students don't have until Term 3 of Year 12, when it is too late to add Methods.

Common misconceptions

"Scaling is decided in advance." No. Scaling is recalculated from scratch each year using that year's cohort data. There are no predetermined outcomes. A subject that scaled up last year can scale flat the next.

"My old marks scale at this year's rates." No. Marks are scaled in the year you sat the course. If you accumulate scaled scores over the previous four years, each is locked at the rate from its own year.

"A combined mark of 65 in Physics = a combined mark of 65 in English." No. Combined marks aren't comparable across subjects. Scaled scores are. A 65 scaled is the same achievement whether the subject is Physics, English, or Dance.

"Hard subject = scaled up." Not directly. AMS scales by cohort strength, not perceived difficulty. Specialist scales up because the people taking it are also crushing their other subjects, not because the syllabus has more content.

Sources: TISC, Marks Adjustment Process for University Admission (Dec 2023); TISC, The Australian Tertiary Admission Rank (ATAR), 2017; Harrison & Hyndman, Modelling the participation function with a one-parameter family of cubic splines (2015).