Distinguish temperature from heat, and use q = mcT to calculate the heat absorbed or released by a substance given its mass, specific heat, and temperature change.
Temperature and heat are related but different: temperature measures the AVERAGE kinetic energy of the particles in a substance, while heat is the actual energy that transfers from a warmer object to a cooler one. Two objects can be at the same temperature but store very different total amounts of heat energy depending on their mass and what they are made of.
Specific heat capacity (c) is a property unique to each substance: the amount of heat energy needed to raise the temperature of exactly 1 gram of that substance by 1 degree Celsius. Water has an unusually high specific heat, 4.184 J/(g x degrees C), which means water resists temperature change far more than most substances -- a large part of why coastal climates stay milder than inland climates, and why a metal spoon in hot soup heats up almost instantly while the soup itself stays hot for a long time.
The heat equation ties it together: q = m x c x deltaT, where q is heat energy (in joules), m is mass, c is specific heat, and deltaT is the change in temperature (final minus initial). A positive q means heat was absorbed by the substance (it warmed up); a negative q means heat was released by the substance (it cooled down) -- the sign is information, not a mistake to erase.
Mastery looks like: They correctly calculate heat absorbed or released using q = mcT, keeping deltaT's sign correct and correctly interpreting the sign of the final answer.
Common stumbles: Subtracting initial minus final instead of final minus initial when finding deltaT; dropping or ignoring the negative sign on q instead of using it to state whether heat was released.