I have long felt, when putting a primary student through an English and Maths assessment, that what I get is in effect a cross-sectional slice of academic reality. The slice is infinitely thinner, proportionally, to the whole than this chunk of ship to its original length, but it is comparable in affording a glimpse of the different 'rooms' of the structure and how they connect one with another.
It may be overdoing the analogy, but an assessment can perhaps be regarded as working round the ship as follows: test for word recognition - the hold; test for reading comprehension - the living quarters; test of free expressive writing (spelling, punctuation, grammar, fluency, handwriting) - the bridge; test of the operations of arithmetic - the engine room; test of problem-solving and general calculating ability - the chart room.
To sail prosperously a ship requires a crew. If there is a equivalent of a crew in the assessment it is the performance itself, the style of the student's working, the willingness and concentration, the manner of addressing the tasks. Taking these into account is what makes an assessment an assessment - not an exam. An exam shows evidence past: tutoring that follows from an assessment entails 'working with the crew'.
Schools of course employ the analogy of a climb, rather than a slice of reality, and model a child's academic progress through the curriculum by ascents from Level to Level. The model carefully records the distinctive features of each new plateau gained.
My approach to Levels on the whole is to let the school take care of them. Parents sometimes inform me of their child's levels in Maths and English, but I don't try to confirm or contest them. The dynamics of the mind are such that no student's performance is ever 'still' enough to be reliably pinpointed in an assessment of 40 minutes, and in any case, a Level designation such as 4C can only ever be an average, with certain aspects of performance being stronger and some weaker.
In my experience the 'slice of reality assessment' does what I ask of it. It shows me roughly where a student is placed in the advancing academic column for their age. It informs me what activities to set when we begin work. And it enables me to sense what learning styles and attitudes I should expect to have to respond to.
Whether the student is industrious and self-starting, or diffident and demotivated, the aim from my perspective is the same - to ensure that the precious time of tuition is exploited to their benefit to the fullest possible extent.