别说……连……也 / 都……, 连……更不用说……: let alone…
【高94】【高98】复句 / complex sentences (递进)
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
别说 A，连 B 也 / 都…… ("let alone A, even B…") and 连 B 也 / 都……，更不用说 A build a climax: the surprising case B already holds, so the case A goes without saying. With 别说 the obvious case comes first: 别说跑步，连走路都累 ("never mind running, even walking tires me"). With 更不用说 the order is reversed: first the extreme case, then the obvious one: 他连这几个字都不会写，更不用说写作文了。
The extreme case is always the one after 连. In 别说是大学生了，连小学生都比他写得好 it is the primary-school pupil, the least likely to write better, who proves the point, so the university student "goes without saying". 别说 here is a fixed phrase ("let alone"): do not confuse it with the imperative 别说了 ("stop talking"). After 连 you need 都 or 也 before the verb. The variant 别说 A，即使 (是) B，也…… carries the same idea in a slightly more written tone.
Compare plain 连……都 (HSK 3), which only says "even", and the more formal 尚且……何况 (HSK 6) and 何况 (HSK 5), often closed by 呢. Both 别说 and 更不用说 work in speech and in writing, and they are a handy debating tool for pushing an argument to its end.
Examples
这间屋子别说放床了，连放一把椅子的地方都没有。
Zhè jiān wūzi bié shuō fàng chuáng le, lián fàng yì bǎ yǐzi de dìfang dōu méiyǒu.Forget a bed: there isn't even room for a chair in this room.
他刚学中文，别说写文章了，连自己的名字都写不好。
Tā gāng xué Zhōngwén, bié shuō xiě wénzhāng le, lián zìjǐ de míngzi dōu xiě bu hǎo.He has only just started Chinese: let alone writing an essay, he can't even write his own name properly.
别说是大学生了，连小学生都比他写得好。
Bié shuō shì dàxuéshēng le, lián xiǎoxuéshēng dōu bǐ tā xiě de hǎo.Never mind university students: even primary-school pupils write better than he does.
他连这几个字都不会写，更不用说写一篇作文了。
Tā lián zhè jǐ ge zì dōu bú huì xiě, gèng búyòng shuō xiě yì piān zuòwén le.He can't even write these few characters, let alone a whole essay.
最近忙得连周末都要加班，更不用说出去旅游了。
Zuìjìn máng de lián zhōumò dōu yào jiābān, gèng búyòng shuō chūqù lǚyóu le.I've been so busy lately that I even work at weekends, never mind going away on a trip.
别说爸爸，即使是老师，也说不出这种植物的名字。
Bié shuō bàba, jíshǐ shì lǎoshī, yě shuō bu chū zhè zhǒng zhíwù de míngzi.Dad, forget it: even a teacher couldn't name this plant.
Common mistakes
✗ 别说小学生，连大学生都比他写得好。 → ✓ 别说大学生，连小学生都比他写得好。 (the case after 连 must be the most surprising one: here the primary-school pupils).
✗ 他连这几个字不会写，更不用说作文了。 → ✓ 他连这几个字都不会写，更不用说作文了。 (连 needs 都 or 也 before the verb).