Five pronunciations, decided by what follows: a consonant, a silent e, an r, an l, or nothing much at all.
Letter sounds
a LETTER_A_01
Useful pattern · Medium reliability · Very common · Early · Reading
/æ/ short a: cat, map, sad
/eɪ/ long a: cake, table, apron
/ɑː/ broad a: father, calm, palm
/ɔː/ a before l: all, ball, talk
/ə/ schwa: about, sofa, banana
Where Wiggler teaches it: Skill 1: First Sounds & Blending · Skill 2: CVC Word Mastery · Skill 6: Magic e · Skill 8: R-Controlled Vowels · Skill 12: Multisyllable Decoding
Child explanation
The letter a has more than one sound. In cat it says /æ/. In cake it says its name. In ball it says /ɔː/. And in about it is barely there at all.
The rule
Try short /æ/ first in a closed syllable. Long /eɪ/ when a silent e or a vowel team follows, or when a lives alone at the end of a syllable. After w and before l, a is usually /ɒ/ or /ɔː/. In an unstressed syllable it is schwa.
What is really going on
Single a is conditioned chiefly by syllable type and by adjacent consonants. In a closed stressed syllable it is /æ/; with a following silent e or in an open stressed syllable it is /eɪ/; before l plus a consonant, and after w, it retracts (all, talk, want, wash); before r it is r-controlled; and in any unstressed syllable it reduces to /ə/. The broad /ɑː/ of father and calm is a small residue plus, in some accents, the bath set.
Position in the word
Stressed syllable — Short in a closed syllable, long in an open one. For example: cat, table, apron, napkin.
Before a consonant — Before l plus a consonant, a retracts: /ɔː/ or /ɑː/. For example: salt, walk, calm, half.
After a consonant — After w or qu, a is usually /ɒ/ rather than /æ/. For example: want, wash, watch, squash.
Unstressed syllable — Schwa, whatever else the word looks like. For example: about, sofa, banana, alone.
Made-up words that follow the rule. A child who reads these has the pattern rather than the vocabulary.
nask, blape, vall
Exceptions
a after w and qu: want, wash, watch, swan, squash, quality. The lip-rounding of /w/ pulls the vowel back, so the expected short a does not appear.
a before r after w: war, warm, ward, dwarf, quarter. The same retraction, this time landing on the or sound.
any → /e/: any, many. A one-off historical spelling; the same vowel appears in many and Thames.
Contrast pairs
cat versus cake — Closed versus silent e.
cat versus car — Closed versus r-controlled.
pal versus ball — Single l versus the -all family.
cap versus want — Short a versus a after w.
Common reading mistakes
ball: a child reads /bæl/, where the word is /bɔːl/. Short a applied inside the -all family.
want: a child reads /wænt/, where the word is /wɒnt/. Short a applied after w.
about: a child reads /æˈbaʊt/, where the word is /əˈbaʊt/. Unstressed a decoded fully instead of reduced.
Do not teach it like this
"A says /æ/."
It is true of a in a stressed closed syllable and of very little else. A child holding that as a rule mis-reads ball, walk, table, want, car and about — all of them common, several of them among the first hundred words.
"A says /æ/ when a consonant shuts it in. Watch what comes after it: e, l, r and w all change it."
Teacher note
Introduce short a first and let it be the only a for a while. Add the others in the order a child meets them: a_e at Skill 6, ar at Skill 8, and the -all / -alk family as a word family rather than a rule. Save schwa a for multisyllable work at Skill 12 — until a child is reading two-syllable words there is nothing for it to apply to.
Accent notes
General American — The bath set — dance, bath, grass, chance, ask — takes /æ/, the same vowel as cat.
British English — The same set takes /ɑː/ in southern varieties: dance rhymes with the vowel of father. Northern British accents use /æ/.
Indian English — Usually follows the British /ɑː/ in dance and bath. Unstressed a is often less reduced than in British or American speech, so banana may keep a fuller vowel in the first syllable — a legitimate accent feature, not a decoding error.