Step 1: Read the goal.
We must select what a teacher's positive attitude develops among $J, K, L, M$.
Step 2: Examine Self-confidence (J).
Encouragement and acceptance help children believe in themselves, so J is a valid outcome.
Step 3: Examine Motivation to learn (K).
A supportive teacher makes learning rewarding, raising motivation, so K is valid.
Step 4: Examine Classroom participation (L).
Feeling safe and respected encourages students to take part, so L is valid.
Step 5: Examine Fear (M).
Fear grows from punishment and negativity, the opposite of a positive attitude, so M is invalid.
Step 6: Combine the valid outcomes.
\[ J + K + L = \text{valid},\quad M = \text{rejected} \]
Step 7: Choose the option.
J, K and L only is option A.
\[ \boxed{\text{A. J, K and L only}} \]