SOLO Taxonomy
A five-level scheme for describing the structural complexity of learner responses, developed by John B. Biggs and Kevin F. Collis in Evaluating the Quality of Learning: The SOLO Taxonomy (Structure of the Observed Learning Outcome) (Academic Press, 1982). SOLO classifies the quality of an observed performance rather than the cognitive operation a task is meant to elicit.
Origin
Biggs and Collis worked from a Piagetian background in Australia, analysing student answers across school subjects. They argued that responses cluster along a single dimension of structural sophistication that can be applied across content areas and ages. The taxonomy is descriptive: levels are read off learner work, not assigned to tasks in advance.
The Five Levels
- Prestructural: the learner misses the point. The response is irrelevant, restates the question, or shows no engagement with task content.
- Unistructural: one relevant aspect is identified or used. Understanding is correct but limited to a single piece.
- Multistructural: several relevant aspects are present, but they remain unconnected. Knowledge is listed rather than integrated.
- Relational: the aspects are linked into a coherent whole. The learner shows how parts relate within the immediate context.
- Extended Abstract: the integrated whole is generalised, transferred, or reframed. The learner moves beyond the given context to principles, hypotheses, or new applications.
The first three levels describe a quantitative shift (more elements known); the move to relational and extended abstract describes a qualitative shift (elements connected and generalised). Biggs has often summarised this as the surface-to-deep learning transition.
Application in ELT
SOLO is widely used to write and grade Learning Outcomes because its verbs map directly onto observable performance.
- Define, identify, name ↔ unistructural
- List, describe, enumerate ↔ multistructural
- Compare, explain causes, integrate ↔ relational
- Generalise, predict, evaluate, hypothesise ↔ extended abstract
In writing assessment, SOLO clarifies why a Task 2 response that lists arguments without connecting them sits at the multistructural level while a response that integrates them into a coherent thesis reaches relational, regardless of vocabulary range. In speaking, the taxonomy distinguishes responses that string facts from responses that link them under a position. SOLO complements Bloom's Taxonomy and the Anderson and Krathwohl Revised Taxonomy: Bloom classifies the cognitive process a task aims to elicit; SOLO classifies the structure the response actually shows.
Limitations
SOLO works best on extended responses where structure is visible and least well on short factual recall. Reliable application requires moderation: raters need shared exemplars, since "relational" judgements vary across markers. The single-dimension claim has been challenged for domains in which sophistication is not unidimensional, but cross-content empirical work has supported the broad ordering.
References
- Biggs, J. B., & Collis, K. F. (1982). Evaluating the Quality of Learning: The SOLO Taxonomy (Structure of the Observed Learning Outcome). Academic Press.
- Biggs, J. B., & Tang, C. (2011). Teaching for Quality Learning at University (4th ed.). Open University Press / SRHE.
- Hattie, J., & Brown, G. T. L. (2004). Cognitive Processes in asTTle: The SOLO Taxonomy. University of Auckland.