教 jiào pictures a lesson: a hand with a rod beside a child. The right element is 攵 (pū), the radical that began as a hand 又 holding a stick or staff, the sign of striking, rapping, or directing. The left side carries the child: the oracle-bone and bronze forms show 子 (zǐ, child) with the marks of the counting-tablet above it, the same elements seen in 孝 (xiào, filial). Put together, the scene is an elder guiding a child through a lesson, rod in hand, the original image of disciplined instruction.

From that one scene the character spreads across a wide field of meaning:

1. To teach, to instruct (jiào). The formal reading, the root of the whole vocabulary of schooling: 教育 jiàoyù (education), 教师 jiàoshī (teacher), 教室 jiàoshì (classroom), 教训 jiàoxun (a lesson, often a hard one).
2. To teach a skill (jiāo). The colloquial reading, used for the everyday act of showing someone how: 教书 jiāoshū (to teach, as a profession), 教中文 jiāo Zhōngwén (to teach Chinese).
3. Teaching, doctrine, religion (jiào). A body of teaching handed down: 宗教 zōngjiào (religion), 佛教 Fójiào (Buddhism), 基督教 Jīdūjiào (Christianity).

The thread running through all of it is transmission: knowledge, a craft, or a faith passed from one who holds it to one who does not. Note the two readings. As a verb of the bare act of teaching it is often jiāo; as a noun for instruction, education, or religion it is jiào.

教 is a polyphone, a character with two readings, and learners meet both early. The split is not random: it tracks how the word behaves. When 教 is the plain verb "to teach," the bare act of showing someone how to do something, it usually takes the first-tone reading jiāo: 我教你 wǒ jiāo nǐ "I'll teach you," 他教数学 tā jiāo shùxué "he teaches math," 教书 jiāoshū "to teach for a living."

When 教 is a noun, or part of a compound naming instruction, education, or religion, it takes the fourth-tone reading jiào: 教育 jiàoyù (education), 教师 jiàoshī (teacher), 宗教 zōngjiào (religion). A handy rule of thumb: if you can put an object after it and mean simply "teach X," reach for jiāo; if it sits inside a settled noun, reach for jiào.

Chinese names religion as 宗教 zōngjiào, literally "ancestral teaching" or "lineage doctrine." The logic is the same thread that runs through the whole character: a religion is a body of teaching handed down. So the name of nearly every faith ends in 教: 佛教 Fójiào (Buddhism, the "Buddha teaching"), 道教 Dàojiào (Daoism), 基督教 Jīdūjiào (Christianity, the "Christ teaching"), 伊斯兰教 Yīsīlánjiào (Islam), 儒教 Rújiào (the Confucian teaching).

The same 教 builds the words for religious places and roles: 教堂 jiàotáng (a church), 教会 jiàohuì (a church as a body of believers), 主教 zhǔjiào (a bishop, "chief teacher"). Throughout, 教 is read jiào and means the teaching itself, the doctrine that a community gathers around and passes to the next generation.

Picture the old scene inside 教: a child on the left, and on the right a hand holding a rod, 攵, raised to direct the lesson. Hold that image of an elder guiding a child, and every sense of the character follows from it. The act itself is to teach (教书, 教中文). Gather it into an institution and it is education (教育, 教师, 教室). Hand it down as a doctrine a whole community lives by and it is religion (宗教, 佛教).

The two readings sort by job. When 教 is the bare verb with an object, "teach me this," it is usually first tone, jiāo. When it locks into a noun for instruction or faith, it is fourth tone, jiào. Ask whether you are doing the teaching or naming the teaching, and the tone follows.