Will heating of KClO3 be considered disproportionation?
Thermal decomposition of potassium chlorate is not disproportionation, just a redox reaction.
Disproportionation refers to the same element acting both as oxidizing agent and a reducing agent, resulting in compounds which contain the same element in different oxidation states.

On the other hand, if you consider preliminary decomposition stage involving perchlorate formation, then it is a disproportionation reaction:

$$\ce{4 K\overset{+5}{Cl}O3 -&gt;[\pu{400 °C}] 3 K\overset{+7}{Cl}O4 + K\overset{-1}{Cl}}$$

Also, synthesis of $\ce{KClO3}$ is a disproportionation reaction:

$$\ce{6 KOH + 3 \overset{0}{Cl}_2 -&gt; 3 H2O + 5 K\overset{-1}{Cl} + K\overset{+5}{Cl}O3}$$