Theory:

The pattern of rhymes at the ending of each line in a poem is called a rhyme scheme. Letters (A,B,C...) are usually used to express which lines rhyme. Verses that are designated with the same letter are said to rhyme with each other. It is also known as an arrangement of rhymes in a stanza or a poem.
Example:
1. For easier understanding of the concept, let us take a famous nursery rhyme, written by Jane Taylor as an example.
 
Twinkle twinkle little star,
How I wonder what you are.
Up above the world so high
Like a diamond in the sky.
We see that the first two lines rhyme with each other (star-are); the second two lines rhyme with each other (high-sky). Let us name each line as  A, B  depending on the words that rhyme with each other.
 
Twinkle twinkle little star,A
How I wonder what you are.A
Up above the world so high,B
Like a diamond in the sky.B
It can thus be seen that this poem follows AABB pattern.
Rhyme scheme of the poem "Your Space" - written by David Bates, is as follows:
 
Speak gently! – It is better farA
To rule by love, than fearB
Speak gently – let not harsh words marA
 The good we might do here!B
  
Speak gently! – Love doth whisper lowA
The vows that true hearts bind;B
And gently Friendship’s accents flow;A
Affection’s voice is kind.B
  
Speak gently to the little child!A
Its love be sure to gain;B
Teach it in accents soft and mild:-A
 It may not long remain.B
  
Speak gently to the young, for theyA
Will have enough to bear –B
Pass through this life as best they may,A
‘T is full of anxious care!B
  
Speak gently to the aged one,A
Grieve not the care-worn heart;B
The sands of life are nearly run,A
 Let such in peace depart!B
  
Speak gently, kindly, to the poor;A
Let no harsh tone be heard;B
They have enough they must endure,A
Without an unkind word!B
  
Speak gently to the erring – know,A
They may have toiled in vain;B
Perchance unkindness made them so;A
Oh, win them back again!B
  
Speak gently! – He who gave his lifeA
To bend man’s stubborn will,B
When elements were in fierce strife,A
 Said to them, ‘Peace, be still.’B
  
Speak gently! – ’tis a little thingA
Dropped in the heart’s deep well;B
The good, the joy, which it may bring,A
Eternity shall tell.B
Important!
The overall rhyme scheme of the poem "Your Space" is \(ABAB\).
Reference:
State Council of Educational Research and Training (2019). Term-1 English Standard-7. Your Space by David Bates (pp. 70-72). Published by the Tamil Nadu Textbook and Educational Services Corporation.