Ordinal numbers are used for indicating order. The following ESL lesson plan explains how to teach English language learners how to form the ordinal numbers in English as well as combining cardinal numbers and ordinal numbers to form decimals and fractions. Also included is a printable download.
Ordinal Numbers

Begin by second part of the number lesson plan by teaching ESL students how to form ordinal numbers. Ordinal numbers are numbers used for indicating order. The majority of ordinal numbers are formed by affixing the -th suffix onto the cardinal number:

   1st – first*
   2nd – second*
   3rd – third*
   4th – fourth
   5th – fifth*
   6th – sixth
   7th – seventh
   8th – eighth
   9th – ninth*
   10th – tenth
   11th – eleventh
   12th – twelfth*
   13th – thirteenth
   14th – fourteenth
   15th – fifteenth
   16th – sixteenth
   17th – seventeenth
   18th – eighteenth
   19th – nineteenth

However, note that first (1st), second (2nd), third (3rd), and fifth (5th) are irregular: first (1st) and second (2nd) must simply be memorized, but third (3rd) and fifth (5th) are related to the spelling and pronunciation changes of the cardinal numbers thirteen (13) and thirty (30) and fifteen (15) and fifty (50). Also point out the slight spelling change in ninth (9th) and twelfth (12th).

For multiples of ten, a final y changes to an ie and then the -eth suffix is affixed to the end of the number:

 
20th – twentieth
   30th – thirtieth
   40th – fortieth
   50th – fiftieth
   60th – sixtieth
   70th – seventieth
   80th – eightieth
   90th – ninetieth

All other numbers above twenty follow the ­-th suffix rule in combination with the rules for the first nineteen numbers and the multiples of ten. For example:

   21st – twenty-first
   100th – one hundredth
   101st – one hundred and first OR one hundred and oneth*
   110th – one hundred and tenth
   1,000th – one thousandth
   1,111th – one thousand one hundred and eleventh
   1,000,000 – one millionth

*The use of oneth in higher ordinal numbers is nonstandard but often used by native English speakers.

 
Decimals

Next introduce the words for the decimals:

   0.X – tenth(s)
   0.0X – hundredth(s)
   0.00X – thousandth(s)
   0.000X – ten thousandth(s)
   0.0000X – hundred thousandth(s)
   0.00000X - millionth(s)

All decimals follow the singular-plural system for English nouns in that the number is spoken as the digit followed by the name of the decimal with any decimal larger than one taking the plural ­–s marker. A period is placed between the whole number and the decimal. For example:

   0.1 – one tenth
   0.2 – two tenths
   0.01 – one hundredth, one one hundredth
   0.33 – thirty-three hundredths
   0.001 – one thousandths, one one thousandth
   0.654321 – six hundred fifty-four thousand three hundred twenty-one millionths

Decimals may also be spoken as whole number-point-digits. Zeros are spoken as zero or oh. For example:

   0.1 – point one, zero point one, oh point one
   1.25 – one point two five
   6.425 – six point four two five
   2.1368 two point one three six eight
   1.057 – one point oh five seven
   4.0098 – four point zero zero nine eight

 
Fractions

Finally teach the ESL students how to form fractions in English. The numerator (the top number) is spoken as a cardinal number and the denominator (the bottom number) as an ordinal number. However, half is used in place of second and sometimes quarter in place of fourth. For fractions in which the numerator is larger than one, the denominator takes the plural -s suffix. English fractions are also written with a hyphen between the numerator and denominator. For example:

   1/2 – one-half
   1/3 – one-third
   2/3 – two-thirds
   1/4 – one-fourth, one-quarter
   4/5 – four-fifths
   99/100 – ninety-nine one hundredths, ninety-nine hundredths

Fractions may also be spoken as cardinal number-over-cardinal number. For example:

   1/2 – one over two
   1/3 – one over three
   2/3 – two over three
   1/4 – one over four
   4/5 – four over five
   99/100 – ninety-nine over one hundred