If you're unsure how to approach modal verbs of obligation, go in prepared with this thorough discovery handout which takes away any uncertainty or nasty surprises and will help mould students' understanding of this important grammar.
1. Copy one handout for each individual student and distribute them.
2. Decide how 'guided' you want the grammar discovery to be. For weak classes go through the entire sheet together with the students, eliciting rules and principles on the board as you go. When necessary, provide the students with the individual 'down time' in order to do the tasks. For medium-ability groups, allow students to go through the sheet individually or in groups and 'intervene' at the end of each section A,B,C etc. Finally for stronger ability groups, get students to work in small groups and elicit the grammatical rules and principles at the end of the sheet orally or by getting students to write on the board.
3. Whichever your approach, allow the students the necessary time to complete the individual sections and ask for feedback for each section.
4. Give students a warning when their time limit is about to expire and then insist on pens down and heads up.
5. For feedback, there are a number of options including students writing some/all of the answers on the board, students orally contributing their answers individually or in groups (which could be scored like a quiz).
6. Draw the students' attention to any specific mistakes which seem prevalent through the discovery and offer language input.
