Methods of teaching comparison of degrees adjective in english

2.1. What students need to know about comparative and superlative adjectives
The first thing students need to know is how to construct comparative and superlative forms. There are no rules which aren’t broken and many adjectives have more than one acceptable form, but there are patterns which are worth knowing. Very basically, short words generally change to “+er/est” and long words change to “more/ most +” (presumably because “petrifying” is quite long enough already and sounds silly as “petrifyinger”). However, most words ending in “-y” change to “-ier/-iest”.
More specifically, one syllable words almost always change to “+er/est” (but with exceptions such as “more fun/ the most fun” and sometimes with the spelling changes below) and words with three or more syllables almost always change to “more/ most +” (but with exceptions such as some words ending in “-y” still changing to “-ier/-iest”) [8.155].
Two-syllable words can go either way, and with quite a lot of two-syllable words both “-er” and “more” are used by different native speakers. However, I have found that “more/ most +” as in “more/ most careful” is more common than “+er/est” in the most useful examples for my students, so I usually include more examples of that pattern in my lessons.
The only other grammar point that might need explaining is doubled letters in the comparative and superlative, something that happens with a stressed short vowel sound followed by a single consonant (“big” becoming “bigger” etc). This is because otherwise the “-er” and “-est” at the end of the word would change the vowel sounds in the same way as “magic E” and make the pronunciations of “biger” and “hotest” “baiger” and “hoatest”, in the same way that “bige” would be pronounced “baig” and “hote” would be “hoat”. This is the same change for the same reason as in “running” and “spotted” (as “runing” and “spoted” would be pronounced “rooning” and “spoated”). Long vowel sounds and diphthongs are not affected by Magic E (“short” and “shorte” being pronounced just the same), and so there is no need to add another consonant sound when adding “-er” or “-est” apart from with short vowels (so it’s simply “shorter” and “shortest”).
Students are often aware of the existence of these rules and are unlikely to stop making mistakes with the forms however long you spend on them, so I tend to very quickly move onto the much more important and neglected topic of collocations with comparative and superlative forms. With comparative forms these are, in approximate order of how big the difference between the two things is:

• 
  very slightly/ a tiny bit + more…/…er
  
• 
  a bit/ a little/ a little bit/ slightly + more…/…er
  
• 
  somewhat + more…/….er
  
• 
  quite a lot/ considerably/ substantially + more…/…er
  
• 
  a lot/ much/ far + more…/…er [7.211-212].
  

With superlative forms collocations include:

• 
  the most…/ the …est + by far/ by a long way
  
• 
  clearly + the most…/ the …est
  
• 
  the most…/ the …est + by a substantial margin/ by a considerable margin
  
• 
  the most…/ the …est + but not by far/ by a small margin
  
• 
  the most…/ the …est + but only just
  

Expressions like “the second warmest” and “the third tallest” might also be useful.
Typical student mistakes with these forms are mainly to do with using collocations that should only go with plain adjectives, such as:

• 
  quite bigger X
  
• 
  very bigger X
  
• 
  extremely biggest X
  

As I said above, I spend much more time on collocations like these than on how to make comparative and superlative forms. As I tell my students, this language is vital if you don’t want to make pointless statements like “That skyscraper is taller than my house”. In addition, using collocations is a great way for students to distinguish themselves from lower level students and to make up for any inevitable mistakes with the use of “-er” etc, especially in language exams like FCE and IELTS. This is also your best hope for stopping students saying “more larger”, as this is often because they actually want to say “much larger”.
Most communicative activities with comparative and superlative forms tend to bring up other comparing and contrasting forms like “less…”, “the least…”, “(not) as… as…”, “in (complete) contrast”, “however” and “whereas”, and I tend to also teach at least a couple of these in most classes on comparative and superlative forms.