A parent raised an interesting issue recently when she asked why students are grouped by ability in a language class - for example, in beginners, intermediate and advanced groups when studying French or Putonghua - but they are not grouped by ability in my biology class, when some students struggle more than others in understanding abstract concepts and biological jargon.
She was referring to the practice of grouping students of similar ability for instructional purposes. Yes, one size does not fit all - so ability grouping can be used for any subject.
But most schools have mixed-ability grouping for science subjects. This is because research shows ability grouping causes students in lower tiers to internalise their label - leading to a self-fulfilling prophecy.
"Then why does ability grouping work for languages?" the parent inquired.
Ability grouping can take several forms. Ability-based groupings "in-class" (such as reading groups within one classroom) or "whole-class" (students are assessed and placed into specific classrooms with peers of similar ability) have received lots of attention in educational research and have also been subject to scrutiny for the inequity they represent.
Studies have found a positive side to grouping. In language classes, research shows that ability grouping allows some students to progress faster. Students then have a better chance of becoming more proficient in the language, compared with students who need to spend more time learning it. When the teachers used ability grouping, the students' assessment scores for reading were significantly higher, showing a positive correlation between ability grouping and reading.
"What other subjects benefit from grouping?" she asked.
In the later years of secondary education, a subject choice (for example, taking math studies over higher math for the International Baccalaureate diploma) in itself results in differentiation by ability.
An observational study by Carol Tieso from the University of Alabama found significant differences in students' maths scores after being placed in ability groups.
"Then why aren't all maths classes in all schools grouped by ability?" this parent reasoned.
Research strongly supports the effects of ability grouping when they are used for enrichment and acceleration. When advanced students are grouped together, there is little impact on self-esteem and, in fact, there is a moderate gain in attitude towards the subject.
But there are negative effects on average and slower learners' social and emotional functions.
Thus, overall achievement effects favour the heterogeneous placement of students in a mixed-ability classroom.
In a special issue of the Harvard Education Letter, guest editors Leon Lynn and Anne Wheelock responded to the query: "Does the homogeneous grouping of students enable the largest number to experience the most success in learning? Or does heterogeneous grouping create a setting in which more students can perform to the best of their abilities?"
Their answer? "Evidence is mounting that schools which reserve the highest quality educational opportunities for the 'best' students - determined by a selection process that is often flawed and discriminatory - are denying many students the opportunity to achieve their full potential."
The parent asked: "How, then, can a teacher help a student achieve his or her full potential in a mixed class?"
By delivering differentiated instruction. This theory recognises that students have different inherent abilities for each subject and thus have different needs. Still, students are expected to master the same concepts, principles and skills.
Teachers can meet the needs of a diverse classroom of students by differentiating instruction in three general areas: the content of the subject; the techniques used to help students make sense of a given topic; and the products that students produce to demonstrate their learning. Anjali Hazari teaches IB and IGCSE biology at the French International School