Geneva Bible Translation Notes1 Chronicles 25

Moreover David and the captains of the host {a} separated to the service of the sons of Asaph, and of Heman, and of Jeduthun, who should prophesy with harps, with psalteries, and with cymbals: and the number of the workmen according to their service was:
(a) The singers were divided into 24 courses, so that every course or order contained twelve, and in all there were 288, as in 1Ch 25:7.

Of Jeduthun: the sons of Jeduthun; Gedaliah, and Zeri, and Jeshaiah, Hashabiah, and Mattithiah, {b} six, under the hands of their father Jeduthun, who {c} prophesied with a harp, to give thanks and to praise the LORD.
(b) Of which one is not here numbered. (c) Meaning, psalms and songs to praise God.

And they cast lots, {d} ward against [ward], as well the {e} small as the great, the teacher as the scholar.
(d) Who should be in every company and course. (e) Without respect to age or cunning.

Now the first lot came forth for Asaph to {f} Joseph: the second to Gedaliah, who with his brethren and sons [were] twelve:
(f) So that he served in the first turn and the rest every one as his turn followed in order.