This is really two senses living under one spelling, separated by a single dot. With a sin (שׂ, dot on the left) the root means intellect, reason, learning: sechel (sense), haskala (education, the Enlightenment), the rationalist. With a shin (שׁ, dot on the right) it means bereavement: to lose one's children, the bereaved parent. Modern Hebrew keeps them apart by the dot and the vowels, but they are written with the same consonants, a reminder that the dot is not decoration, it is meaning. The 'cluster' (eshkol) and 'grapefruit' (eshkolit) ride along on the shape too. Every word is verified against pealim, niqqud included.
The same root runs through the verb system. Each binyan is a voice: it bends the one idea into active, passive, causative or reciprocal. Tap to hear.
The two binyanim split along the dot: the pa'al לִשְׁכֹּל (with shin) is the bereavement verb; the hif'il לְהַשְׂכִּיל (with sin) is the intellect verb (to gain education, to act wisely). They sound close but mean opposite worlds, the dot and the vowels keep them apart. The nif'al, pi'el and passive moulds are not lexicalized for this root.
Same root letters, different noun moulds (mishkalim). The mould tells you the function: who does it, the act of doing it, or the thing produced.
Strip the prefixes, suffixes and vowels. Three consonants remain, and the meaning lives there.